Image reading device

ABSTRACT

An image reading device includes light-emitting diode chips ( 11 A- 11 C) and a light guide ( 3 ) having a main region ( 3 A) and a subsidiary region ( 3 B). The subsidiary region ( 3 B) includes a light incident surface ( 31 ) located above the light source ( 11 A- 11 C) and an inclined surface ( 32 ). The light source ( 11 A- 11 C) is offset in a direction receding from the main region ( 3 A) with respect to the center (C 2 ) as viewed in the primary scanning direction of the light incident surface ( 31 ).

TECHNICAL FIELD

The present invention relates to an image reading device for reading animage on a document, for example.

BACKGROUND ART

An example of an image reading device for reading an image printed on adocument is disclosed in JP-A-H12-125080, for example. The conventionalimage reading device is described below with reference to FIGS. 5 and 6of the present application.

As shown in FIG. 5, the image reading device 100 includes a light source120 and a light guide 130. The light guide 130 guides light from thelight source 120 to an image reading area S.

Specifically, the light guide 130 includes a subsidiary region 130 a anda main region 130 b. The subsidiary region 130 a includes a lightincident surface 131 for entrance of the light from the light source120, and an inclined surface 132 for shifting the traveling direction ofthe light entering through the light incident surface 131. The mainregion 130 b includes a main reflecting surface 133 for shifting thetraveling direction of the light, which traveled from the subsidiaryregion 130 a to the main region 130 b, toward the image reading area S,and also includes a light emitting surface 134 for emitting the lighttoward the image reading area S. As shown in FIG. 6, the main reflectingsurface 133 includes a plurality of recesses 135. The recesses 135,spaced from each other in the primary scanning direction (indicated byan arrow AB), shift the traveling direction of the light entering intothe recesses 135, toward the image reading area S.

The light source 120 is a light-emitting diode (LED) chip. As shown inFIG. 6, the light passing portion of the light source 120 is positionedright below the center of the light incident surface 131 of the lightguide 130 in the primary scanning direction. This arrangement is madefor attaining uniform irradiation to the light incident surface 131 withthe light from the light source 120.

In the image reading device 100, one way to increase the lightirradiation toward the image reading area S (thereby obtaining ahigh-quality image) is to increase the amount of light emission from thelight source 120.

However, the increase in the light emission from the source 120 entailshigher power consumption at the light source 120, which is notdesirable.

DISCLOSURE OF THE INVENTION

The present invention has been proposed under the above-describedcircumstances. An object of the present invention is to provide an imagereading device for regulating the power consumption at a light source,while increasing the amount of light irradiation toward an image readingarea.

An image reading device according to the present invention comprises: alight source; and a light guide including a main region extending in aprimary scanning direction and a subsidiary region contacting with anend of the main region. The subsidiary region includes a light incidentsurface located above the light source. The subsidiary region furtherincludes an inclined surface that is inclined toward the main region asproceeding upward, so that light entering the light incident surface andthen traveling upward is reflected generally horizontally toward themain region. The main region includes a light emitting surface and amain reflecting surface provided with a light reflector for reflectingthe light traveling from the subsidiary region to the main region, sothat the light is emitted from the light emitting surface. The lightsource is offset in a direction receding from the main region withrespect to a center of the light incident surface in the primaryscanning direction.

Preferably, the image reading device according to the present inventionfurther comprises a base plate on which the light source is mounted.

Preferably, the image reading device according to the present inventionfurther comprises a resin packaging cover for accommodating the lightsource. The resin packaging cover includes a body made of a white resinand a light passing portion made of a transparent resin for causinglight from the light source to emit from the resin cover.

Preferably, the light source includes a plurality of light-emittingdiode chips arranged in an array extending in a secondary scanningdirection.

Preferably, the light-emitting diode chips include a red diode, a greendiode, and a blue diode.

Preferably, the main region of the light guide include a pair of sidesurfaces extending between the main reflecting surface and the lightemitting surface. The side surfaces are parabolic and have a main axiscoinciding with a line centered widthwise of the main region.

Preferably, the surfaces of the light guide are mirror-finished.

Preferably, the image reading device according to the present inventionfurther comprises a reflector held in contact with the light guide.

Preferably, the light reflector includes a plurality of recesses spacedfrom each other in the primary scanning direction.

Other features and advantages of the present invention will be apparentfrom the following description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a section view illustrating an image reading device accordingto the present invention.

FIG. 1B is an enlarged view illustrating a principal part of FIG. 1A.

FIG. 2 is a section view taken along lines II-II of FIG. 1A.

FIG. 3 is a perspective view illustrating a light source shown in FIG.1.

FIG. 4 is a perspective view illustrating a light guide shown in FIG. 1.

FIG. 5 is a section view illustrating an example of a conventional imagereading device.

FIG. 6 is a section view illustrating a conventional light guide.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of the present invention is described below withreference to FIGS. 1-4.

As shown in FIGS. 1-2, an image reading device X according to thepresent invention includes a light source 1, a case 2, a light guide 3,a reflector 4, a transparent plate 5, a lens array 6, a plurality ofsensor IC chips 7, and a base plate 8.

As shown in FIG. 3, the light source 1 includes three LED chips 11A-11C,a first electrode 12, second electrodes 13, and a packaging cover 14.The light source 1 is mounted on an upper surface 81 a of an end 81 ofthe base plate 8 (see FIG. 1A).

The first and the second electrodes 12, 13, made of an electroconductivemetal such as copper, are spaced from each other in the primary scanningdirection (indicated by an arrow AB). The first and the secondelectrodes 12, 13 include portions exposed out of the cover 14, andthrough the exposed portions, are electrically connected to wiringpatterns (not shown) on the base plate 8. In the present embodiment, useis made of three second electrodes 13 spaced from each other in thesecondary scanning direction (indicated by an arrow CD). The number ofthe electrodes is an example, and the present invention is not limitedto this.

The LED chips 11A-11C are mounted on the first electrode 12corresponding to the second electrodes 13 respectively, and emit lightrays of different colors. Specifically, as shown in FIG. 1B, the LEDchips 11A-11C are disposed nearer to the end 81 of the base plate 8 inrelation to a center C1 of the light source 1 in the primary scanningdirection, while being aligned in an array extending in the secondaryscanning direction (the arrow CD) as shown in FIG. 3. The LED chips11A-11C upwardly emit red, green, and blue light rays. Each of the LEDchips 11A-11C is electrically connected to the corresponding secondelectrode 13 via a wire W made of gold, for example.

The cover 14 includes a body 140 and a light passing portion 141 throughwhich light is emitted from the cover 14. The body 140 is made of awhite resin having high light reflectance, while the light passingportion 141 is made of a transparent resin (e.g. epoxy resin) havinghigh light permeability.

As shown in FIG. 1A, the case 2 is elongated in the primary scanningdirection (the arrow AB). The case 2 includes first and secondaccommodation spaces 21, 22. The first accommodation space 21accommodates the light source 1, the light guide 3, and the reflector 4.The second accommodation space 22 accommodates the sensor IC chips 7.The case 2 further includes a light shield 23. The light shield 23separates the case into the first accommodation space 21 and the secondaccommodation space 22, and also prevents the sensor IC chips 7 fromdirectly receiving light from the light source 1 or from receiving lighttraveling in the light guide 3. The case 2 is made of a synthetic resin,for example.

The light guide 3 includes a main region 3A elongated in the primaryscanning direction and a subsidiary region 3B connected to an end of themain region 3A. The subsidiary region 3B guides light emitted from theLED chips 11A-11C to the main region 3A. The main region 3A causes thelight traveling from the subsidiary region 3B to be emitted toward animage reading area S. The light guide 3 is made of a material havinghigh transparency, such as PMMA (polymethylmethacrylate). The surfacesof the light guide 3 are mirror-finished. Due to this, the lighttraveling in the light guide 3 can be totally reflected on the mirrorsurfaces.

The subsidiary region 3B includes a light incident surface 31 forentrance of light emitted from the light source 1. The subsidiary region3B further includes an inclined surface 32 for causing the lightentering through the light incident surface 31 to proceed into the mainregion 3A. As well shown in FIG. 1B, the light incident surface 31includes a center C2 in the primary scanning direction that is arrangedright above the center C1. The LED chips 11A-11C are offset in adirection receding from the main region 3A with respect to the center C2of the light incident surface 31. The surface 32 is inclined in a mannersuch that it comes closer to the main region 3A as proceeding upwardfrom its bottom end 32 a contacting with an end 31 a of the lightincident surface 31, until its top end 32 b comes into contact with themain region 3A. The inclined surface 32 is curved such that the lighttraveling upward from the light incident surface 31 is reflected intohorizontal light proceeding toward the main region 3A.

As shown in FIG. 4, the main region 3A includes a main reflectingsurface 33 at the lower portion of the light guide 3 and a lightemitting surface 34 facing to the image reading area S. The main region3A further includes a pair of side surfaces 35 extending between theabove-mentioned surfaces 33, 34. The main reflecting surface 33 isprovided with a plurality of recesses 33 a spaced from each other in theprimary scanning direction (the arrow AB). The recesses 33 a scatter thelight traveling in the main region 3A. Each recess 33 a is elongatedwidthwise of the main region 3A and arcuate in section. The sidesurfaces 35, having a common main axis L coinciding with the widthwisecenter line of the main region 3A, cooperate to form a parabolicsurface. As shown in FIG. 2, the side surfaces 35 further have a commonfocus O1 on or in the vicinity of the main reflecting surface 33. Withsuch an arrangement, the light reflected on the recesses 33 a and theside surfaces 35 can be emitted toward the image reading area S from thelight emitting surface 34 as a bundle of rays substantially parallel tothe main axis L of the side surfaces 35.

The reflector 4 is formed with a groove 40 for holding the light guide3. The reflector 4 covers the light guide 3 except for the lightincident surface 31 and the light emitting surface 34, therebypreventing light leakage from portions other than the light emittingsurface 34. The reflector 4 is made of a white synthetic resin havinghigh light reflectance, for example.

The transparent plate 5 is attached to the upper surface of the case 2.The transparent plate 5 serves as a paper guide when a document D istransferred in the secondary scanning direction (arrow CD) by a platenroller P. The transparent plate 5 may be made of a synthetic resin orglass.

The lens array 6 focuses the reflection light from the document D ontothe sensor IC chips 7. The lens array 6, elongated in the primaryscanning direction, includes a synthetic resin holder 61 and a pluralityof imaging lenses 62 held in an array within the holder 61.

Each of the sensor IC chips 7 is an elongated rectangular semiconductorchip having a photoelectric converting function, and includes a lightreceiver 71 for receiving light. The sensor IC chip 7 outputs imagesignals corresponding to the amount of light received at the lightreceiver 71. The sensor IC chips 7 are mounted on the base plate 8 rightbelow the lens array 6.

The base plate 8 is attached on the lower surface of the case 2 andprovided with connectors (not shown) for external power supply and forinput-output of various signals. The upper surface of the base plate 8is formed with wiring patterns (not shown) for electrically connectingthe above-mentioned connectors to the light source 1 and to the sensorIC chips 7. The base plate 8 is made of ceramic, for example.

Next, the function of the image reading device X is described below.

As shown in FIG. 1, the LED chips 11A-11C of the image reading device Xemit light, and the light enters into the subsidiary region 3B throughthe light incident surface 31 of the light guide 3. The light enteringinto the subsidiary region 3B is reflected on the inclined surface 32,and then enters into the main region 3A. The light entering into themain region 3A travels in the primary scanning direction (the arrow AB)as being totally reflected in the main region 3A. Meanwhile, the lightis reflected on the recesses 33 a (see FIG. 4) serving as a lightreflector, and then emitted from the light emitting surface 34 towardthe image reading area S.

As described above, the LED chips 11A-11C of the image reading device Xare offset from the center C2 of the light incident surface 31 in thedirection receding from the main region 3A. With such an arrangement,the light entering substantially perpendicular to the light incidentsurface 31 is reflected by the inclined surface 32 at portions lowerthan the reflecting portions of the conventional image reading device.As a result, the light reflected by the inclined surface 32 travels inthe main region 3A along paths that are closer to the main reflectingsurface 33 than in the conventional image reading device. It should benoted here that the light ray entering substantially perpendicular tothe light incident surface 31 has the greatest brightness among lightrays emitted from the LED chips 11A-11C. Thus, in the image readingdevice X, the light ray with the greatest brightness travels near themain reflecting surface 33. In this way, the amount of light raysreflected on the recesses 33 a is larger than that of the conventionaldevice, and the amount of light rays emitted from the light emittingsurface 34 is also increased. As a result, the light irradiationefficiency at the image reading area S of the image reading device X ishigher than the light irradiation efficiency of the conventional imagereading device.

In the present invention, the recesses of the main reflecting surface 33may be replaced with projections. Further, the main reflecting surface33 may be provided with a coating which enables scattering reflection oflight.

The present invention being thus described, it is obvious that the samemay be modified in various ways. Such modifications should not beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to those skilled in the artare intended to be included in the scope of the appended claims.

1. An image reading device comprising: a light source; and a light guideincluding a main region extending in a primary scanning direction and asubsidiary region contacting with an end of the main region; wherein thesubsidiary region includes a light incident surface located above thelight source, and an inclined surface that is inclined toward the mainregion as proceeding upward, so that light entering the light incidentsurface and then traveling upward is reflected generally horizontallytoward the main region, wherein the main region includes a lightemitting surface, and a main reflecting surface provided with a lightreflector for reflecting the light traveling from the subsidiary regionto the main region, so that the light is emitted from the light emittingsurface, wherein the light source is offset in a direction receding fromthe main region with respect to a center of the light incident surfacein the primary scanning direction.
 2. The image reading device accordingto claim 1, further comprising a base plate on which the light source ismounted.
 3. The image reading device according to claim 1, furthercomprising a resin packaging cover for accommodating the light source,the resin packaging cover including a body made of a white resin and alight passing portion made of a transparent resin for causing light fromthe light source to emit from the resin cover.
 4. The image readingdevice according to claim 1, wherein the light source includes aplurality of light-emitting diode chips arranged in an array extendingin a secondary scanning direction.
 5. The image reading device accordingto claim 4, wherein the light-emitting diode chips include a red diode,a green diode, and a blue diode.
 6. The image reading device accordingto claim 1, wherein the main region of the light guide include a pair ofside surfaces extending between the main reflecting surface and thelight emitting surface, the side surfaces being parabolic and having amain axis coinciding with a line centered widthwise of the main region.7. The image reading device according to claim 6, wherein the surfacesof the light guide are mirror-finished.
 8. The image reading deviceaccording to claim 1, further comprising a reflector held in contactwith the light guide.
 9. The image reading device according to claim 1,wherein the light reflector includes a plurality of recesses spaced fromeach other in the primary scanning direction.